1. Field of the Invention
The present invention relates to the recovery of hydrogen from gas mixtures and, more particularly, to a method for obtaining increased hydrogen recovery from oil refineries and petrochemical or natural gas operations by combining a steam reformer hydrogen product stream with an offgas stream and utilizing the combined stream as feed for a single pressure swing adsorption (PSA) unit.
2. Description of the Related Art
The use of pressure swing adsorption (PSA) to separate gas mixtures is well known in the art. More specifically, it is known that one or more PSA units can be used to recover hydrogen from streams containing mixtures of hydrogen and hydrocarbons in refineries and petrochemical operations. For example, it has been previously proposed that a single PSA unit be utilized within a refinery or petrochemical operation to recover hydrogen from a flow stream. U.S. Pat. No. 5,435,836 by Anand et al. titled “Hydrogen Recovery By Adsorbent Membranes” shows a single PSA unit being used to treat a steam-methane reformer product stream. Similarly, U.S. Pat. No. 5,507,856 by Rao et al. titled “Hydrogen Recovery By Adsorbent Membranes” shows a single PSA unit being used to treat a combined stream made up of a steam-methane reformer product stream and a refinery waste stream. It has also been previously proposed that multiple PSA units be utilized within a refinery process to promote increased hydrogen recovery. For example, Patent No. WO0027505 by Ravi and Satish titled “Recovery of CO2 and H2 from PSA Offgas in an H2 Plant” shows a gas separation process in which multiple PSA units are utilized.
However, these and other previously proposed arrangements for hydrogen recovery using PSA units suffer from a number of disadvantages. For example, in the case where multiple PSA units are being utilized to treat different feed streams, if some portion of the feed stream for one of the PSA units was to exceed the capacity of the PSA unit, the excess portion is not effectively utilized to promote hydrogen recovery. Instead, the excess portion is typically sent to flare or burned as fuel gas elsewhere in the refinery. Another disadvantage of previously proposed arrangements using multiple PSA units is that in order to achieve maximum hydrogen recovery, each PSA unit must be operated at or near maximum capacity. Operating these units at such high capacity damages the adsorbent material within the units by increasing the likelihood that impurities will be carried over between adsorbent layers. Also, operating some of these PSA units at or near maximum capacity requires an increased feed stream and fuel gas stream for the unit operation providing the feed stream, which raises operating costs.
Accordingly, prior to the development of the present invention, there has been no single method of hydrogen recovery in refineries and petrochemical operations in which some or all of the feed streams from separate PSA units were combined and utilized as feed for a single PSA unit, and in which some or all of a steam reformer product stream and a refinery offgas stream being used as feed streams for separate PSA units were combined and utilized as feed for a single PSA unit, and in which total hydrogen recovery was increased by maximizing hydrogen recovery from refinery offgases, and in which the load on the steam reformer was reduced by lowering the reformer feed stream, and in which refinery fuel gas consumption was reduced in the steam reformer furnace, and in which the amount of excess gases from a PSA feed stream being burned as fuel or sent to flare was reduced, and in which the load on the PSA unit receiving feed from refinery offgases was reduced, and in which the hydrocarbon content and heating value of the tail gas from the PSA unit fed by the steam reformer product stream was enriched.
Therefore, the art has sought a method of hydrogen recovery in refineries and petrochemical operations in which some or all of the feed streams for separate PSA units are combined and utilized as feed for a single PSA unit, and in which some or all of steam reformer product and refinery offgas streams being used as feed streams for separate PSA units are combined and utilized as feed for a single PSA unit, and in which total hydrogen recovery is increased by maximizing hydrogen recovery from refinery offgases, and in which the load on the steam reformer is reduced by lowering the reformer feed stream, and in which refinery fuel gas consumption is reduced in the steam reformer furnace, and in which the amount of a PSA feed stream being burned as fuel or sent to flare is reduced, and in which the load on the PSA unit receiving feed from refinery offgases is reduced, and in which the hydrocarbon content and heating value of the tail gas from the PSA unit fed by the steam reformer product stream is enriched.